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# AD9081:maximum input data rate of Main Datapath for case Mtx=2

Hello,
I have a question about the AD9081 for the case of Mtx equal to 2.
Оn table-98 of UG-1578,  the input data rate is 6GSPS at fDAC=12GSPS.
The above says "The maximum input data rate into the HB3 filter is limited
to 4 GSPS. When using this filter, select the MTX according
to the target fDAC so that the 4 GSPS limit at the input of
HB3 is not exceeded."

But according to Figure 75, the HB3 filter cannot be bypassed.
What is the maximum transmission rate of the Main Datapath in the case of M equal to 2?

• Hi VFRANTOV,

TB1 can be bypassed:

- when using HB4 (4x or 8x interp)

- when using only HB3 (2x interp)

Regarding the max transmission rate with main DP interp = 2x:

- Downstream of the interpolation filters (right side in the diagram), all the blocks are running at Fdac

- Upstream from the interp filters, the blocks would run at Fdac/M_tx = Fdac/2

Landsman

• Hi Landsman,

For the case of Mtx equal to 2, the hb3 filter is enabled and all other filters are disabled.

Since the maximum data entry rate into the HB3 filter is limited to 4 GSPS, the maximum Fdac frequency is limited to 8 GHz (Mtx=2). This does not correspond to the data given in the table 98 (Fdac= 12GHz, input data rate = 6 GSPS).

Where am I wrong?

• Hi VFRANTOV,

You are right. In my reply I misread HB3 as "3x". HB3 can only be bypassed if interp=1x.

Let me look into this and I will get back to you.

Landsman

• Hi VFRANTOV,

Both snippets of information are accurate, although there is some details missing. We'll plan to add it to the next UG revision. in short, the input datarate depends which HB3 is being used (in which main datapath):

 Datapath connects to: DAC0 DAC1 DAC2 DAC3 Filter type: 80%BW-85dB-6GSPS 90%BW-70dB-4GSPS 80%BW-85dB-4GSPS 80%BW-85dB-4GSPS 90%BW-70dB-4GSPS 80%BW-85dB-4GSPS Max input datarate and BW: 4GSPS @ 90%BW 6GSPS @ 80%BW 4GSPS @ 80%BW 4GSPS @ 90%BW 4GSPS @ 80%BW

In order to support 6GSPS I/Q the JESD204C must run near its max lanerate across all 8 lanes, so having more than one datapath support 6GSPS is not really needed: running two 6GSPS IQ channels is not really possible due to max link speed.

I hope this helps :)

Landsman